A disc brake is conventionally used for an automotive brake. The conventional disc brake uses a disc brake pad as a frictional member, where the friction material is affixed on a metal base member.
Japanese Provisional Patent Publication Number 2006-275198 (Patent Document 1) discloses the disc brake pad formed by affixing the friction material including the fiber base material, the binder, and the filler on a back plate, where the friction material has straight phenolic resin and phenol aralkyl resin as the binder in mass ratio of 85:15-65:35. This disc brake pad enables to maintain the durability under the high load conditions and to reduce brake noise, cracking around an end portion of junction between the friction material and the back plate, and peeling of the friction marital from the back plate.
Recently, in order to improve automotive fuel efficiency and operability, lightweight automotive components are in demand. To accomplish the goal of producing lightweight components, there are proposals to lower the density of materials used to make components and parts and to reduce the thickness and to minimize the component size, and particularly for brake components there is a demand to downsize brake system, especially the disc rotor.
Downsizing the disc rotor while maintaining brake efficiency and capacity at the same level without downsizing is required, and therefore the friction material on the disc pad used in combination with the disc rotor would have to bear greater loads due to the downsizing of the disc rotor. Accordingly, the friction material needs to have a higher fading resistance.
In order to improve the fading resistance of the friction material, in some cases, cryolite has been added to the friction material. However, the friction material with cryolite has a problem of sticking the friction material with the disc rotor when dissolving cryolite at a surface portion of the friction material when temperature of the friction material becomes high, and under this condition, if a tight contact between the friction material and disc rotor is maintained, as the friction material temperature falls, dissolved cryolite solidifies to adhere the friction material and the disc rotor.
Japanese Provisional Patent Publication No. 2009-132816 (Patent Document 2) discloses a non-asbestos friction material including a fiber base material, binder, lubricant, and other fillers, where the fillers at least contains calcium pyrophosphate. Furthermore, the Patent Document 2 discloses non-asbestos friction material including the above-mentioned calcium pyrophosphate of 4-6 volume % and cryolite of 3-5 volume % as the filler.
The sticking problem considered due to cryolite may be restricted effectively by the technology of the Patent Document 2; however, another sticking problem without cryolite became apparent.
Patent Document 1: Japanese Provisional Patent Publication No. 2009-132816. Patent Document 2: Japanese Provisional Patent Publication No. 2009-132816